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Help Troubleshoot, Please?

OK, 1988 R100RS, 81,000 relatively troublefree miles. It's white if that matters.
A few days ago, my bike was reluctant to start in 45 degree weather. Previously it would start in the coldest weather, even 20 degrees. So as the day warmed up, it started right up at about 55 degrees. Three times in the last few days, after starting and about 1/2 mile down the road, the engine dies. Just dies. And it doesn't start right back up immediately.
Has gas, has a battery that is always on a tender. Plenty of ability to turn over the engine.

Here is a kicker before someone tells me it's grounding out. After that one time per outing when it dies and it warms up. it does not die which makes me think it's not electrical.
What defies logic is why both cylinders die simultaneously which does make it seem electrical in nature. Snowbum's carb page states that my reported symptom is characteristic of needle and jet wear. Dying shortly after starting.

Anyone have a similar experience?

Rick

"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." Mark Twain

Are you getting spark? Don't do the grounding to the head thing with your electronic ignition, that will likely make matters worse. Use an inductive timing light or in line plug checker. They both fire sinultaneously.
Both the ignitor on the frame and the "bean can" are heat sensitive. if you are getting no spark, the ignitor is vastly cheaper. But I have had 3 bean cans, but only one ignitor, die in past 5 years.
I vote this is electrical issue.
Jiggle your key in there when it won't restart, it is possible your ignition switch innarrds are disintegrating. Ditto the kill switch.

About 3 years ago, I had a similar problem, but not so much with starting. The bike would just stop, sometimes at very inconvenient places. Sometimes it would start right back up, sometimes it wouldn't. It was losing spark. There was an issue with wiring. I couldn't sort it out, but my mechanic did. He ended up replacing a wiring harness. The old one had been hacked and spliced so many times, that it was really the best option.

I'm thinking this is less related to the actual ambient temps and more related to some electrical problem. It's a 25 year old motorcycle, wires get stretched and corroded over time. Electrical/spark issues have cropped up mutliple times over the years on my 36 year old RS. I've owned this bike almost 13 years now. In that time, I've replaced the starter, the battery (twice), wiring harness, left handlebar switchgear, horn relay, starter relay, and other minor wiring issues. I've also replaced the plug wires and plugs, but that was more of just doing maintenance.

Are you getting spark? Don't do the grounding to the head thing with your electronic ignition, that will likely make matters worse. Use an inductive timing light or in line plug checker. They both fire sinultaneously.
Both the ignitor on the frame and the "bean can" are heat sensitive. if you are getting no spark, the ignitor is vastly cheaper. But I have had 3 bean cans, but only one ignitor, die in past 5 years.
I vote this is electrical issue.
Jiggle your key in there when it won't restart, it is possible your ignition switch innarrds are disintegrating. Ditto the kill switch.

Actually, I timed it with a light last week.

Rick

"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." Mark Twain

I'm on board with Baron, if you haven't adjusted the valves recently, your timing isn't "correct". I'd recommend adjusting the valves, and then re-adjusting the ignition timing. If you can get it go for a 20+ mile run, synchronize your carburetors when you get back and the engine is good and hot. Chances are that this will not solve your sudden-death syndrome but at least the basics will be correct and can be eliminated from the mix.

Fuel consumption over a half-mile ride doesn't sound like enough to cause the tank to vacuum lock due to a plugged gas cap vent, but it might be something else (that's easy) to check. Just a though on this; if your tank is fully topped-up the volume of air remaining above the fuel might be small enough to allow vacuum lock to occur...

But both cylinders dying simultaneously ... certainly does sound e-lek-trickle.

"It is what you discover, after you know it all, that counts." _ John WoodenLew Morris
1973 R75/5 - original owner
1963 Dnepr

Perhaps a poor choice of terms. Vacuum lock, or vapor lock, usually is associated with warm/hot temps. But it wouldn't make any difference at all what the temperature was if the gas cap vent was plugged.

"It is what you discover, after you know it all, that counts." _ John WoodenLew Morris
1973 R75/5 - original owner
1963 Dnepr

My 1988 R100RS exhibited the exact same symptoms some years ago - for no apparent reason it would just quit, sometimes at high speed. After a little while it would start right back up and run well until the next time it quit.

Took it to the dealer a couple of times before they diagnosed that the spark plugs wires were bad. After the plug wires were changed I never had the problem again.

I meant, is there spark when this occurrence happens, and you can't get it started? Issues with the ignitor, bean can, or especially ignition switch can appear and disappear seemingly randomly. It makes no difference if you had successfully adjusted timing recently, where the failure event is somewhat random. If you take an inline spark checker with you, you can check for spark right after it dies and won't start. Then you can eliminate, or focus on, your electrics.